Sleep-wake disturbances are frequently looked at as “symptom clusters”—groups of interrelated symptoms that can occur simultaneously and interact with each other to cause additional symptoms or worsen existing ones. Symptoms from cancer and its treatment have been studied as clusters only since around 2001 (Beck, Dudley, & Barsevick, 2005).

Pain, Sleep Disturbance, and Fatigue
These three symptoms are intricately and logically linked. Cancer-related pain may cause patients to have insomnia symptoms, including increased sleep latency (difficulty falling asleep), reduced sleep efficiency (decreased amount of time spent asleep or total time in bed), or increased number and length of nighttime awakenings. Insomnia symptoms can cause fatigue symptoms, or worsen existing cancer-related fatigue. Although insomnia and fatigue are not directly linked to pain, the presence of these in conjunction with pain has been shown to predict a higher symptom burden (Beck et al., 2005).

Gedaly-Duff, Lee, Nail, Nicholson, and Johnson (2006) looked at this symptom cluster in children receiving chemotherapy for acute lymphoblastic leukemia. They found that in the three days after receiving outpatient chemotherapy, the children reported experiencing all three symptoms. Sleep disturbance occurred in the form of increased nighttime awakening. Gedaly-Duff et al. (2006) also had the children’s parents record their own symptoms; the parents also had increased awakenings, but not as many as the children. The findings suggest that managing patients’ sleep symptom clusters may also improve sleep-wake disturbances in caregivers.

Pain, Sleep Disturbance, and Depressive Symptoms
As with the first symptom cluster, a link exists among pain, sleep disturbance, and depressive symptoms. The link between pain and sleep disturbance is well established; McMillan, Tofthagen, and Morgan (2008) explained that in their analysis, the common tie was distress—patients felt distressed by the pain experience and distressed by having sleep disturbances. Pain is similarly related to depressive symptoms; as pain interferes with a patient’s activities of daily living, the patient has increased depressive symptoms (McMillan et al., 2008).

Fatigue, Sleep Disturbance, and Depressive Symptoms
Because fatigue and sleep disturbance are linked, as are sleep disturbance and depressive symptoms, logically a relationship exists among all three. Carpenter et al. (2004) looked at these symptoms in breast cancer survivors and in healthy menopausal women experiencing hot flashes. All of the participants had high rates of sleep disturbance, but the survivors had more nighttime hot flashes and significantly shorter sleep duration than the healthy women. Despite this, overall sleep quality was similar for both groups. The authors noted that in their study, sleep disturbance correlated with fatigue and depression but not frequency of hot flashes.

According to Beck et al. (2005), when a symptom is part of a cluster, all symptoms in that cluster must be addressed to achieve full symptom management. For example, in a pain, fatigue, and sleep disturbance symptom cluster, if pain and fatigue are addressed without consideration of sleep disturbance, symptom management will be suboptimal.